BlockContentTypeDeleteForm.php

<?php

namespace Drupal\block_content\Form;

use Drupal\Core\Entity\EntityDeleteForm;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides a confirmation form for deleting a block type entity.
 *
 * @internal
 */
class BlockContentTypeDeleteForm extends EntityDeleteForm {

  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $block_count = $this->entityTypeManager
      ->getStorage('block_content')
      ->getQuery()
      ->accessCheck(FALSE)
      ->condition('type', $this->entity
      ->id())
      ->count()
      ->execute();
    if ($block_count) {
      $caption = '<p>' . $this
        ->formatPlural($block_count, '%label is used by 1 content block on your site. You can not remove this block type until you have removed all of the %label blocks.', '%label is used by @count content blocks on your site. You may not remove %label until you have removed all of the %label content blocks.', [
        '%label' => $this->entity
          ->label(),
      ]) . '</p>';
      $form['description'] = [
        '#markup' => $caption,
      ];
      return $form;
    }
    else {
      return parent::buildForm($form, $form_state);
    }
  }

}